1. Field of the Invention
The present invention relates to an air bag apparatus assembled in a steering wheel or the like of a vehicle and which develops and inflates a bag body in a direction toward a vehicle occupant to protect that vehicle occupant.
The present invention, while explained with reference to an embodiment of an air bag apparatus for a steering wheel, it can be equally applied to other air bag apparatus for an assistant driver's seat or a rear seat having a similar structure.
In this specification, each of the terms "vertical", "lateral" and "longitudinal", which shows a relationship between positions means a relative relationship between positions from a viewpoint in front view of the steering wheel with the vehicle going straight ahead.
2. Description of Related Art
Air bag apparatus usually includes an inflator, an air bag mounted to the inflator in a folded state, from an original circular shape, and a cover for covering the folded bag body. The cover is provided with a hinged door portion which opens by a force applied at a time when the air bag is initially developed and inflated.
On the basis of the present demand, in which the air bag of the air bag apparatus is preferentially developed and inflated in a vertical direction, an example of such, an air bag apparatus is described in Japanese Patent Publication No. 7-110600.
This air bag apparatus for a driver's seat is mounted to a substantially central portion of a steering wheel and comprised an inflator for generating a gas for developing an air bag. The air bag is arranged in a folded body state and surrounds a gas injection hole of the inflator, it has a circular shape when inflated and is covered by a cover member capable of suddenly breaking open.
The cover member included an upper flap which opens to an upper side of the steering wheel and a lower flap which opens to a lower side of the steering wheel.
In some cases a center line which agrees with the direction in which the upper and lower flaps of the cover member are broken and developed, passes through a center point of the air bag is defined as Y, and that a center line which crosses the center line Y in a perpendicular direction and passes through a center point of the air bag is defined as X,
The air bag is formed with a long and narrow shape in the Y direction by folding right and left side surfaces disposed in right and left side of the center line Y to a side of the seated occupant along a first folding line parallel to the center line Y.
Each of the side surfaces of the long and narrow shape, disposed in both side of the center line X, is folded to the side of the seated occupant along a second folding line parallel to the center line X so as to form the folded body having an upper surface and a lower surface which respectively open in an upper direction and a lower direction at an initial time of developing.
However, as a result of inflation testing of the foregoing air bag apparatus performed by the inventors of the present invention, it is found that there is a fast a change of the speed of an inflation between the time when the air bag body is in a middle position and when the air bag body is completely inflated (hereinafter refer to "inflation speed in the middle portion height").
Though it is necessary for the air bag body to completely inflate within a predetermined time, it is preferable that the inflation speed be slow in the middle portion until full inflation is completed.